The subject matter of the present application is related to that of the assignee""s companion application entitled KNIFE AND APPARATUS FOR CLAMPING A KNIFE, of Loren R. Schuh and Tobias L. Simonsen, incorporated by reference herein in its entirety.
The present invention relates to a method and apparatus for clamping a knife in a wood chipper, such as a disc, drum or conical head chipper, for use in the commercial processing of logs.
In wood chipping apparatus used in the forest products industry, a rotating member is provided for receiving replaceable knives for cutting chips from the log. Each knife is typically clamped to the rotating member between an outer clamping member and an inner clamping member or counterknife, wherein the knife and counterknife together form a surface against which the log is forced to remove chips from the log. The chips themselves have commercial value, and their removal shapes the log into lumber and finishes its surface.
A preferred knife for use in such apparatus is manufactured by Key Knife, Inc., of Tualatin, Oreg. (xe2x80x9cKey Knifexe2x80x9d), and described in Schmatjen, U.S. Pat. No. 5,819,826, herein incorporated by reference in its entirety. For convenience when referring to the ""826 patent, terminology employed therein will be used herein as well to describe selected features of the preferred knife.
The knife is elongate and symmetrical about a plane that includes the elongate axis, to provide two cutting edges of the knife. Therefore, either of the cutting edges may be selected for cutting by appropriate installation of the knife. Particularly, when one of the cutting edges is dulled, the knife may be removed from the apparatus, turned end-to-end, and placed back into the apparatus to obtain a fresh cutting edge, providing an outstanding advantage over knives having a single cutting edge.
The knife includes a front side which, when the knife is installed in the apparatus, confronts the counterknife, and a back side which confronts the outer clamping member. Each cutting edge of the knife defines a line terminating two plane surfaces that form an angle with respect to one another, known in the art as the knife angle. The front side of the knife contains one each of the aforementioned plane surfaces (termed xe2x80x9clower knife-edge-joining portionsxe2x80x9d) and the back side of the knife contains one each of the other of the plane surfaces (termed xe2x80x9cupper knife-edge-joining portionsxe2x80x9d).
The front side of the knife further includes a pair of symmetrically disposed deflector ridges projecting therefrom, and extending in the direction of the elongate axis. The deflector ridges are spaced from the respective cutting edges and terminate the respective lower knife-edge-joining portions.
The front side of the knife still further includes a pressure-applying surface portion between the deflector ridges. The pressure-applying surface portion makes contact with a corresponding feature of the counterknife when clamping the knife in the apparatus. Typically, the lower knife-edge-joining portions and the pressure-applying surface portion all lie in a single plane.
Grinding machines are employed to form the aforementioned surfaces. The time required for the grinding operation depends on the number of knives that can be ground by the machine at one time, and this number depends on the size of the knives. The present inventor has recognized that it would be desirable to reduce the width of a knife to reduce the size of the knife and, therefore, manufacturing time and cost.
However, the distance from the cutting edge of the knife to the respective deflector ridges is determined by the requirements of the chipping apparatus and may not be reduced without impacting the performance of the apparatus. On the other hand, reducing the width of the pressure-applying area destabilizes the contact between the knife and the counterknife.
A prior art counterknife manufactured and marketed by Key Knife, Inc. provides a contact point between the knife and counterknife that is outside of the space between the deflector ridges, more particularly 0.583xe2x80x3 from the closest one of the deflector ridges. This counterknife permits the use of a knife having a narrower pressure-applying area, providing for decreased manufacturing costs, while maintaining stable contact with the knife.
In what has heretofore been an unrelated consideration, chipper knives are angled with respect to the wood being cut, wherein the angle is known to be important to chip quality. As mentioned, the angle between the upper and lower knife-edge-joining portions defines the knife angle. The knife when clamped in the apparatus also defines an angle known in the art as the xe2x80x9cattack angle,xe2x80x9d and a xe2x80x9crelief anglexe2x80x9d that is the difference between the attack angle and the knife angle. Adjustment of one or more of these angles is desirable to account for changed conditions, such as changes in the wood or changes in environmental factors such as temperature and humidity.
The typical prior art method for effecting such adjustments is grinding the upper knife-edge-joining portion, which alters the knife angle and relief angle. The attack angle is not altered by this grinding.
Prior art knives provided by Key Knife, Inc. are distinguished from other prior art knives in having the pressure-applying area for contacting the counterknife effectively recessed into the knife. For example, in knives with deflector ridges the pressure-applying area is recessed with respect to the deflector ridges, and in an earlier form of the knife a recessed keyway was provided for the pressure-applying area. Accordingly, the counterknife contacts the pressure-applying area in a region that is outside of the path of the moving chips so that packing cannot occur.
The present inventor has recognized that altering the knife angle and attack angle permits better optimization of chip quality than altering the knife angle and relief angle as is done in the prior art. The contemplated alteration or modification requires altering the angle between the lower knife-edge-joining portions and the counterknife. Where one of the lower knife-edge-joining portions of a knife having two cutting edges makes contact with the counterknife, such as in the aforementioned Key Knife, Inc. counterknives, altering the knife and attack angles has heretofore required modifying or changing the counterknife as well.
Accordingly, there is a need for a method and apparatus for clamping a knife that provides for decreasing manufacturing costs for the aforedescribed knife, particularly by decreasing the width of the knife, as well as providing for changing the attack angle merely by changing the knife, without impacting the performance of the chipping apparatus employing the knife or destabilizing the contact between the knife and the counterknife.
A method and apparatus for clamping a knife according to the present invention solves the aforementioned problems and meets the aforementioned needs by providing a knife having front and back sides wherein the front side includes a recess extending along an elongate axis of the knife, the front side terminating in respective cutting edges of the knife, and outer and inner clamping members for clamping the knife therebetween. The width of the recess divided (xe2x80x9cnormalizedxe2x80x9d) by the distance between the cutting edges yields a result that is preferably no more than about 0.31.
The outer clamping member is adapted to receive the back side of the knife, and the inner clamping member is adapted to receive the front side of the knife, the inner clamping member making contact with the front side of the knife at two spaced locations thereon, wherein at least one of the locations is outside the space between the deflector portions a distance from the closest of the deflector portions, wherein the distance normalized by the aforementioned distance between the cutting edges, yields a result that is preferably no more than about 0.22 from the closest of the deflector portions.
Preferably, the recess is defined by two spaced apart deflector portions and the inner clamping member includes a complementary recess for receiving one of the deflector portions. Preferably as well, the back side of the knife includes a depression and the outer clamping member includes a corresponding projection adapted to fit into the depression and establish a third location of contact for clamping the knife.
Therefore, it is a principal object of the present invention to provide a novel and improved method and apparatus for clamping a knife.
It is another object of the present invention to provide a method and apparatus for clamping a knife that provides for reduced cost of manufacturing the knife.
It is still another object of the present invention to provide a method and apparatus for clamping a knife that provides for decreasing the width of the knife without impacting the performance of the chipping apparatus employing the knife.
It is yet another object of the present invention to provide a method and apparatus for clamping a knife that provides for decreasing the width of the knife without destabilizing the contact between the knife and the counterknife.
It is a further object of the present invention to provide a method and apparatus for clamping a knife having two cutting edges that provides for changing the attack angle of the knife without requiring that the counterknife be changed as well.
It is still a further object of the present invention to provide a method and apparatus for clamping a knife having two cutting edges that provides for changing the attack angle of the knife without requiring that the counterknife be changed as well, and without impacting the performance of the chipping apparatus employing the knife.
It is yet a further object of the present invention to provide a method and apparatus for clamping a knife having two cutting edges that provides for changing the attack angle of the knife without requiring that the counterknife be changed as well, and without destabilizing the contact between the knife and the counterknife.
The foregoing and other objects, features and advantages of the present invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the following drawings.